Decaffeinated instant or soluble coffees represent a significant segment of the coffee market. There are many techniques disclosed in the art for making such products. The preferred techniques will be those that produce a high quality product and are economical to operate. The speed with which the decaffeination is effected and the degree to which caffeine is selectively removed during the decaffeination step are both factors in determining the quality and cost of these systems.
The removal of caffeine from green coffee beans is a technique which has been widely practiced in the art; however, this process requires several hours and involves high temperatures. The removal of caffeine from aqueous coffee extract has been recognized as providing a relatively rapid caffeine extraction step at relatively lower temperatures. The latter process also results in a higher yield and reduced operating costs when compared to the decaffeination of green coffee beans.
Decaffeination of aqueous coffee extract with a water-immiscible organic solvent is normally referred to as liquid-liquid extraction. In such a decaffeination process, roast and ground coffee extract is normally flowed countercurrently to the organic solvent. The solvent removes the caffeine from the coffee extract to provide a decaffeinated extract. The decaffeinated extract is stripped of residual solvent and then processed further to form a decaffeinated instant coffee product. See U.S. Pat. No. 2,933,395 to Adler et al., issued Apr. 19, 1960, which discloses a countercurrent extract decaffeination process.
Direct decaffeination of roast and ground coffee extract can be an effective and efficient method for removing caffeine from the coffee. For example, in countercurrent extract decaffeination, the coffee extract is usually dispersed in the form of small droplets through a continuous solvent phase. The small droplets present a large surface area to the solvent. Because of the large surface area, mass transfer of caffeine from the coffee extract to the solvent is significantly increased. Because of the increased mass transfer, extract decaffeination can become a truly continuous decaffeination process.
While techniques for decaffeinating roasted coffee extracts are more efficient than methods for decaffeinating green coffee beans, there remain certain drawbacks to the former techniques. One such drawback is that the organic solvents used for caffeine extraction do not extract only caffeine from the coffee extract stream. The use of a highly selective solvent (i.e., a solvent which removes only caffeine from the coffee material) would, of course, be highly desirable. However, caffeine solvents presently available for conveniently removing caffeine from coffee extract unavoidably remove some non-caffeine solids from the extract along with caffeine. The failure to recover these non-caffeine solids by returning them in some manner to the dried coffee product necessarily results in a loss of coffee flavor and a reduction in the economic efficiency of the overall process.
In the absence of a highly selective liquid solvent, there have been prior attempts to separate the material removed from the coffee extract into caffeine-rich and essentially caffeine-free solvent fractions. The caffeine-free fraction would then be added back to the coffee extract stream to recover these valuable non-caffeine solids. The caffeine-rich fraction would be removed from the decaffeination system as a waste stream, although the caffeine may desirably be isolated and sold as a valuable by-product of the decaffeination process. One such caffeine recovery method is disclosed in U.S. Pat. No. 2,508,545 to Shuman. Another such method is disclosed in U.S. Pat. No. 2,472,881 to Bender.
Attention in the field has only recently been directed toward the recovery of these important non-caffeine solids. For example, Belgian Pat. No. 865,488 of Bolt et al., issued Oct. 2, 1978, describes a process wherein the coffee extract is first decaffeinated with a water-immiscible organic solvent; the organic solvent is then contacted with water to transfer the caffeine and unavoidably, some non-caffeine solids; the decaffeinated solvent is returned to the coffee extract; residual solvent is stripped therefrom; and the caffeine is crystallized from the water phase, which is then discarded. The water phase inevitably contains some non-caffeine solids which would contribute important body notes to the soluble coffee but are instead discarded. A similar though supposedly improved method is disclosed in U.S. Pat. No. 4,409,253 to Morrison et al. The improvement consists of recyclying the water phase from which the caffeine has been crystallized back to the original caffeine-containing extract. The water phase apparently cannot be combined with the decaffeinated extract because the crystallization leaves substantial caffeine in the water. Hence, the inefficient recycle of the water phase through the decaffeination step is disclosed, with the accompanying increase in the amount of caffeine to be removed.
A different approach has been disclosed, French Pat. No. 1,591,756 to Societe des Produits Nestle S.A., whereby coffee extract is stripped and then decaffeinated with the solvent ethyl acetate; the caffeine-containing ethyl acetate is simultaneously contacted with water and water-saturated ethyl acetate to transfer the caffeine to the water; the caffeine is then crystallized from the water phase which contains no non-coffee solids according to the disclosure; the caffeine-free ethyl acetate is passed through an evaporation step which serves to separate the solvent from the non-caffeine solids and aromatic components; the non-caffeine solids and aromatic components are dissolved in ethyl alcohol and added back to the decaffeinated extract which subsequently passes through a stripping step to remove traces of ethyl acetate. The method is restricted to ethyl acetate for the decaffeination of coffee extracts and trichloroethylene for tea extracts.
It is an object of the present invention to provide a roasted coffee extract decaffeination method which produces a soluble coffee of improved flavor.
It is another object of the present invention to increase the total coffee solubles yield of an extract decaffeination process.
It is a further object of the present invention to provide an efficient means for partitioning non-caffeine solids from caffeine and recovering the non-caffeine solids in the finished coffee product without requiring the recycle of the addback stream through the decaffeination step.
These and other objects of the present invention are disclosed hereinafter.